1. Field of the Invention
The present invention is related to a wireless communication system and a communication method, which are adaptable to slot diversity in order to improve wireless communication qualities in the TDMA-TDD system.
2. Description of the Related Art
Very recently, among wireless telephone apparatus for communicating voice signals in wireless manners, TDMA-TDD (time division multiplex access) type digital communication systems such as DECT system and PHS system have gradually constituted a major wireless telephone system from analog communication systems. In this TDMA-TDD system, for instance, while a frame having a constant time is equally subdivided into “N” pieces of slots (time slots), both a transmission signal and a reception signal are multiplexed in each of equally-divided time slots, and then, a multiplex communication operation is carried out between a mother appliance and a child appliance in a digital telephone system.
Also, in the IMS band, TDMA-TDD type communication apparatus have been developed and are operable in such a frequency hopping system for performing a communication operation while frequencies to be used are sequentially changed.
Preventing a deterioration of communication qualities, which is caused by wireless interference during wireless communications, may constitute an important aspect. Generally speaking, TDMA type communication apparatus using the frequency hopping system employ a so-called “channel swapping method” capable of suppressing an error occurrence caused by wireless interference. In the above-described channel swapping method, a portion of channels usable in a communication operation is set as a replace-purpose reserve channel, and then, a wireless communication is carried out under better wireless condition while the channels (frequencies) other than the reserve channel are switched in a predetermined sequence. When a wireless quality of a channel under use is deteriorated, such a notification that this deteriorated communication channel is replaced by the reserve channel is made with respect to a communication counter party, and the communication operation is continued.
On the other hand, Japanese Patent Publication No. Hei-7-28248 discloses the frequency diversity in the time division wireless communication system. That is, in this frequency diversity system, as to such a communication system (namely, frequency hopping system) that a plurality of frequencies are employed and communication operation is carried out while the frequencies are switched every slot within 1 frame, all of signals of the respective slots within 1 frame are made equal to each other, and the same signals are transmitted by changing the carrier frequencies in a temporal aspect. It should be noted that one of times which are segmented within 1 frame is refereed to as a “slot.” Also, this disclosed technique may also be referred to as a “slot diversity technique”, because not only the frequencies are changed, but also the same signals are transmitted by employing a plurality of slots within 1 frame.
On the other hand, in a wireless communication system which is arranged by a mother appliance operated by a commercial power supply and a child appliance which is connected to this mother appliance in a wireless manner and is driven by a battery, when a slot diversity control operation is carried, since large power consumption is required, there is such a problem that a portability of the child appliance is deteriorated due to lowering of communication time. In the above-explained slot diversity control operation, in order to improve a wireless communication quality, wireless signals which have been modulated by the same transmission data are transmitted in two, or more slots within the same frame from one communication apparatus, whereas the other communication apparatus receives the wireless signals of these plural slots, and then reproduces such a wireless signal having a better communication quality. Also, even under better electromagnetic wave environment, since the above-explained slot diversity control operation is carried out, unnecessary electric power is consumed.